Methods that first form a liquid film on the substrate that is subsequently decomposed are collectively referred to herein as metalorganic solution decomposition (MOSD). The de Rochemont et al. patented art further instructs that molecular-level chemical uniformity within the deposit can be generated when the liquid aerosol is sprayed onto a substrate heated to temperatures in the range of 200° C. to 500° C., preferably in the range of 250° C. and 450° C. In this instance, the thermal energy imparted by the heated substrate to the liquid aerosol is sufficient to initiate the simultaneous decomposition of all metalorganic precursor species contained within the aerosol spray, thereby replicating within the deposited oxide the same level degree of precursor subdivision contained in the metalorganic solution. Metalorganic solution deposition (MOSD) is well represented in the prior art. Alternative methods utilize solution precursor methods to apply a liquid precursor film using spin-coating or spray misting at ambient temperatures. The deposited liquid film is later pyrolyzed into the desired material using a subsequent heating or drying step. These two-step processes are susceptible to phase segregation and the creation of micro-nuclei in multi-component films that can adversely affect the creation of uniform ceramic microstructure. The multi-component liquid film consists of assayed quantities of the distinct molecular precursor species for each of the various metal oxide components desired in the multi-component film. Each distinct molecular precursor species will have a different decomposition temperature. The organic ligand(s) to which a particular metal species is attached to form the molecular precursor will deflagrate and produce the residual metal oxide molecule when it is heated above its respective decomposition temperature. Phase segregated micro-nuclei are created when the temperature of the multi-component liquid film is ramped from ambient temperatures to temperatures that pyrolyze the varied precursor species. Molecular precursors that deflagrate at lower decomposition temperatures will form their respective oxide molecules initially and separate out of the liquid film during their phase change and form micro-clusters of single species oxides or partially mixed oxides as the liquid film is ramped through temperatures that convert some, but not all, of molecular precursors to their residual oxides. Additionally, the molecular precursors having the most robust decomposition temperatures will be last to change into an oxide phase, and will typically do so as an unevenly distributed oxide shell upon the previously formed single species or mixed oxide micro-clusters. The molecular-level chemical uniformity achieved in the liquid phase is subsequently lost during the thermal bake out phase. The resultant non-uniform chemical distribution of oxide components produces conditions with non-uniform chemical kinetics and grain growth at nucleation sites where crystalline phases of the ceramic are formed by post-deposition thermal or radiant heat processing.
Budargin, L., in U.S. Pat. No. 7,211,292 B1 and US2002/0041928 A1, and Budaragin, L, et al. U.S. Pat. No. 7,718,221, is used to form high complexity material laminates by first applying a liquid precursor solution at ambient temperatures (≦50° C.) to form a liquid film that is subsequently converted into a metal oxide by heat treatments at temperatures greater than 400° C. As explained below, this two (2)-step process causes phase separation in the deposit through the sequential decomposition of the component precursor.
McMillan et al. (U.S. Pat. Nos. 5,456,945; 5,540,772; 5,614,252; 5,759,923; 5,888,583, hereinafter referred collectively as McMillan et al.) disclose methods and apparatus for disposing liquid precursor films by flowing a mist of liquid metalorganic precursors over a substrate contained within a deposition chamber, where both the substrate and the deposition chamber are held at substantially ambient temperatures. Although this art instructs the use of liquid precursors comprising wet chemistry techniques that include carboxylic acid and alkloxide chemistries to form silicon dioxide and other oxide dielectrics, such as barium strontium titanate (BST), on integrated circuit substrates, the inventors repeatedly advise that heating the deposition chamber and substrate during the deposition process leads to inferior quality films. Under McMillan et al., ambient temperatures must be maintained within the deposition chamber, which may alternatively be held under vacuum or at atmospheric pressure during the deposition process. General ambient temperatures are clearly defined as ranging between −50° C. and 100° C., preferably ranging between 15° C. and 40° C. The initial deposit is a liquid film that is subsequently dried and treated to form a solid oxide layer. Solvents contained within the liquid film are primarily extracted from the deposit using vacuum techniques. Furthermore, in U.S. Pat. No. 5,759,923, McMillan et al. only instruct on a need for water-free alkoxide chemistries when depositing silicon dioxide materials, suggesting that silicon carboxylic acid chemistries can be exposed to water-containing chemical species or atmospheric environments having relatively humidity, such as ambient air. Additional prior art that instructs the application of a liquid film to a substrate by means of an aerosol spray, followed by solvent extraction and subsequent treatment is cited by Hayashi et al. (US Pub. No. 2002/0092472 A1).
Various deposition systems have been developed as industrial processes to form advanced material laminates on a variety of different substrates. These processes include: chemical vapor deposition (“CVD”), atomic layer deposition (“ALD”), physical vapor deposition (“PVD”), evaporation, and molecular beam epitaxy (“MBE”), among others. Each provides benefits and drawbacks relative to the objective of forming compositionally complex materials at low costs.
Chemical vapor deposition (CVD) techniques are often a preferred method for fabricating layered material structures and is cited frequently in the prior art. CVD introduces vapor phase organometallic or metalorganic precursors into the deposition chamber using a carrier gas and can form deposits at relatively high deposition rates (1-10 μm per hour) by pyrolyzing the precursors on the surface of a heated substrate. Many high quality oxide dielectrics often comprise a plurality metal oxide components, and the ability to disperse various precursors within a vapor cloud in the reaction chamber allows multiple components to be subdivided (intermixed) at the molecular level and benefits compositional uniformity. However, the wide ranging vapor pressures (differing by order of magnitude) and decomposition temperatures (often separated by hundreds of degrees Celsius) of the different precursors makes it difficult to maintain compositional uniformity and control in multi-element deposits. In these instances, minor perturbations in temperature across the substrate surface or as a function of time during the deposition cycle can alter localized vapor pressures among varied precursors that subsequently generate localized fluctuations in the deposit's chemistry, which, in turn, disrupts atomic-scale uniformity of the final deposit and cause defects that impairs manufacturing yield in high tolerance applications. These effects limit CVD's ability to the reliable production of moderate complexity materials (comprising 3-4 elemental components). It has proven to be ineffective when processing high complexity materials.
Paz de Araujo et al. (U.S. Pat. Nos. 6,110,531 and 6,511,718) instruct an enhanced chemical vapor deposition (CVD) technique that gasifies liquid precursor solutions comprising metalorganic precursors that may contain metal alkoxide or metal carboxylate chemical species in whole or in part prior to introducing said gasified precursor solutions into a deposition chamber that contains substrates heated to a temperature ranging between 400° C. and 600° C. (Paz de Araujo '531) and 300° C. and 600° C. (Paz de Araujo '718).
ALD mitigates some of the problems associated with CVD's limitations with regards to forming compositionally complex materials by sequentially introducing one precursor at a time into the reaction chamber. The pulsed gases are injected in quantities that are only sufficient to form an atomic layer on the heated substrate surface. Lower deposition rates and limitations on ultimate layer thickness of the deposit are trade-offs when using ALD. As vapor phase methods, CVD and ALD processes will coat the entire substrate surface. Consequently, additional processing steps, such as photolithography/etch or masked surface preparations, are required to pattern the resulting laminate or deposit it in selective surface areas.
PVD bombards the surface a “target” (the source material) with ionized inert gases to dislodge surface atoms from the target that then diffuse on the surface of a substrate to form the deposit. This technique is generally unsuitable for multiple component materials. MBE is an analog to PVD for what ALD is to CVD. While it greatly improves the quality of multiple component materials, the deposition rates are so low that this tool is generally unaffordable for anything but research.
The high substrate temperatures (>500° C.) required by all of the above mentioned industrial process is another major drawback. This thermal energy is sufficient to nucleate the microstructure of the deposited film to grain sizes that destroy the ability to produce laminate that have nanoscale properties. While plasma-enhanced variants of these processes are reported to form deposits at substrate temperatures lower than 500° C. These claims misinform the public because while the substrate may be set to lower temperature the high thermal energy of the “hot” plasma applied to the substrate's surface causes the temperature of the applied precursors and deposited materials to be driven to much higher temperature without necessarily heating the entire substrate. Substrate surface temperatures in the range of 500° C. to 1000's ° C. are typical of plasma-enhanced processes. These enhanced surface temperatures drive nucleation process in the deposited materials beyond the ability to maintain amorphous or nanoscale microstructures.
Furthermore, all of the above referenced processes have been unable to integrate mismatched materials with layer thicknesses greater than sub-micron physical dimensions without cracking and delamination.